1. Field of the Invention
This invention relates to an apparatus for measuring color values of prints for performing a shading correction of image data obtained by imaging reference plates with an imaging device, and to a shading correcting method.
2. Description of the Related Art
A known such apparatus is disclosed in Japanese Unexamined Patent Publication No. 8-98023. This apparatus includes an imaging device for imaging objects, and a sensitivity adjusting device for adjusting sensitivity of the imaging device based on reference values obtained by imaging a white reference plate and a black reference plate. The apparatus can thereby obtain proper color values from the objects.
In order to reduce spoilage, an actual printing operation may be carried out such that printing is performed at low speed after starting the printing until the printing stabilizes, and at high speed after the printing attains stability. Further, printing speed may be adjusted as appropriate according to the thickness of printing paper and the like. When, with the printing speed varied as above, densities or colorimetric values (hereinafter collectively called “color values”) of prints are measured while the prints are transported, a device is used for varying intervals for imaging the prints (hereinafter called sampling intervals) in order to equalize resolution. As a result, when print transport speed is changed, the amount of color value data obtained by imaging the prints at predetermined sampling intervals varies even if the prints are identical. Therefore, the apparatus described in Japanese Unexamined Patent Publication No. 8-98023 cannot obtain proper color values of the prints, despite the sensitivity adjustment, when reference paper and the prints are transported at different speeds.
On the other hand, Japanese Patent Publication No. 2-57772 discloses a technique for correcting color values to proper values by multiplying actually detected color values by a ratio between a transport speed in time of reference measurement of prints and a transport speed in time of inspection.
However, the color value and transport speed are not necessarily in exact proportionality. It is therefore impossible to correct color values to proper values only by multiplying actually detected color values by a ratio between a transport speed in time of reference measurement of prints and a transport speed in time of inspection.